Field of the Invention
The present invention relates generally to magnetic memory systems having magnetic tunnel junctions (MTJs) that store binary data and particularly to programming of the MTJs.
Description of the Prior Art
Magnetic random access memory (MRAM) is rapidly gaining notoriety as its use in replacing conventional memory is showing promise. Magnetic tunnel junctions (MTJs), which are essentially the devices storing information, include various layers that determine the magnetic behavior of the device. An exemplary MTJ uses spin torque transfer to effectuate a change in the direction of magnetization of one or more free layers in the MTJ. That is, writing bits of information is achieved by using a spin polarized current flowing through the MTJ, instead of using a magnetic field, to change states or program/write/erase/read bits. Currently, the problem with MRAMs are their size. Obviously, reducing the size of a MRAM cell is highly desirable.
Moreover, increasing memory capacity by stacking more than one MTJ on top of another provides great value in terms of costs and real estate on a semiconductor or chip. To this end, writing to or programming of stacked or multi-state MTJs is needed. The current state of technology does not allow for writing or programming a stack of MTJs.
Thus, the need arises for a magnetic memory array to include an array of magnetic memory made of MTJs having small cell sizes and a method and apparatus for writing to a stack of MTJs made of more than one MTJ.